Coordinating Cooling Fans

ABSTRACT

In one example in accordance with the present disclosure a system for coordinating cooling fans in a housing includes a first fan for cooling a power supply; a second fan; a control board to provide a first pulsed wave modulated (PWM) signal to the second fan; and a logic element to provide a control signal to the first fan based on a second PWM signal from the power supply and a third PWM signal from the control board.

BACKGROUND

One challenge in electronic devices is that the high frequency operationcan produce significant heating. Heat can impact the performance andreduce the lifetime of electronic components and devices. In order tomitigate the effects of heat, some electronic devices include fans tocirculate air over the electronics. This reduces the temperature of theair over the electronics, which increases the temperature differentialbetween the electronics and air. The temperature differential is onefactor in the transfer of heat between the electronics and air, withlarger differentials producing greater heat transfer. Thus, thecirculation of air by a fan allows more effective heat loss for theelectronic components

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various examples of the principlesdescribed herein and are a part of the specification. The illustratedexamples are merely illustrative and do not limit the scope of theclaims. Like numerals denote like but not necessarily identicalelements.

FIGS. 1A-C show a structure consistent with one example of the currentspecification with three different air flow patterns produced bydifferent fan control conditions.

FIGS. 2A-B show example structures consistent with the currentspecification.

FIG. 3 shows examples of PWM signals and their possible interactionsusing an OR-logic consistent with the current specification.

FIGS. 4A-B are flowcharts showing example methods of coordinating apower supply fan with other fans in a housing consistent with thecurrent specification.

FIG. 5 shows a structure consistent with one example of the currentspecification.

DETAILED DESCRIPTION

Fans are often used to increase air circulation across electronics inorder to cool the electronics. Fans increase the air pressure on oneside of the fan and reduce the air pressure on the other side of thefan. These air pressures then induce airflow, with air flowing away fromthe high pressure area and towards low pressure areas. However, whenmultiple fans exist in proximity to each other, interaction between thepressures produced by the individual fans may produce unstable,undesirable, and/or less efficient airflow arrangements. In suchcircumstances, coordination of the fans may allow better use of the fansor minimize the energy consumed by the fans to achieve a desired airflowand cooling.

An electronic device typically includes a number of electroniccomponents in a housing. Examples include a desktop tower, laptop case,tablet enclosure, phone, or similar enclosure. Some components may becomposed of a number of subcomponents, including, in some cases, a fanfor cooling the component. For example, a power supply, which convertsstored or received power to desired voltages may include a dedicatedfan. In many instances, such a power supply is a commercially availabledesign which lacks available externally accessible controls in order toregulate the included fan. This presents a challenge in trying tocoordinate the activity of a power supply fan with other fans that maybe installed in the housing of the electronic device, such as a fanassociated with the control panel.

In some examples, the power supply fan is oriented so as to draw airfrom inside the housing, over the power supply, and blow the air out avent or opening in the housing. The fan includes an electric motor whichturns the fan and converts electricity into mechanical work. Theelectrical motor may be capable of being operated at more than one levelof output, generally by varying the voltage supplied to the electricalmotor. Thus, higher voltages applied to the motor cause the motor toturn the fan faster and produce greater airflow. Adjusting the voltagethat is applied to the motor implies a way to control the fan.

While use of a variable transformer, rheostat, and other solutionsexist, one solution is to use a constant voltage signal that is providedat controlled intervals. This is called pulse width modulation (PWM). Ifthe frequency of the pulse is selected appropriately, the devicereceiving the PWM signal interprets the PWM signal as a steady signalrather than reacting to the pulses. For electric motors, this frequencyis generally in excess of 1-10 kHz. When designed appropriately, anelectric motor receiving PWM signal with a duty cycle of X % at Y voltsreacts as if it were receiving a direct current (DC) of X % multipliedby Y volts. Thus, for example, a 5-volt signal that is provided with a40% duty cycle powers the electric motor as if it received a 2-voltdirect current.

One advantage of PWM control is that it tends to have relatively lowlosses. The use of PWM control also has the advantage that the voltagesource remains constant and the duty cycle is adjusted to produce arange of effective voltages on the electric motor. Part of the reasonthis works is the lag in the elements powering the motor aresignificantly longer than the switching time in the PWM signal. Thus,the motor and the fan cannot react fast enough to respond to thevariation in the PWM signal and instead experiences the composite resultof the PWM signal. Accordingly, a PWM signal can be used to providecontrol as well as power for an electric motor driving a fan.

In some examples, the PWM signal is provided as a control signal that isused to control a switch or other connection between a power source andthe fan. In these cases, the PWN signal may have an amplitude that isdifferent from the maximum voltage applied from the power source, forexample, 1-volt vs. 5-volts. In other examples, the PWM signal isprovided as the power signal. In these cases, the maximum amplitude ofthe PWM signal and the maximum power applied may be the same. The use ofa lower voltage control signal may reduce power consumption in somedesigns. However, generally speaking, PWM control signals tend to befairly efficient compared with other methods of scaling voltage.

Power Management Bus (PMBus) is an open standard power-managementprotocol. For power supplies with a PMBus, an interface exists toprovide direct control over the fan from the control panel. However, fornon-PMBus power supplies, there may not be available control access todirectly control the power supply fan. In this specification, a systemand method are disclosed for controlling the fan in a non-PMBus powersupply by combining a second PWM signal with the PWM signal from thepower supply to the fan. The second PWM signal is may be provided by thecontrol panel and allows the control panel to coordinate operation ofthe power supply fan with other fans in the housing of the electronicdevice.

FIG. 1A shows an example of a system (100) consistent with the presentspecification. An enclosure (110) provides mounting locations for afirst fan (120) and a second fan (130). When both the first fan (120)and the second fan (130) are powered at similar, low voltages, the flowfrom both fans is to push air from the inside of the enclosure (110) tothe outside of the enclosure (110). This is consistent with a lowcooling demand condition.

However, as shown in FIG. 1B, when one of the fans, in this case thefirst fan (120), is powered at a low level and the other fan, in thiscase the second fan (130), is powered at a higher level, the airflow ofthe second fan (130) dominates the airflow of the first fan (120) andthe airflow may reverse through the first fan (120). If the first andsecond fans (120, 130) are located so as to increase airflow overelectronics or other components, this inversion of the desired flowpattern results in less efficient cooling as air warmed by passage nearthe first fan (120) is now passed through the second fan (130) and usedfor cooling near the second fan (130) rather than using unheated air. Asthe heat transfer rate depends upon the temperature differential betweenthe heat source (e.g. electronics) and heat sink (surrounding air), theuse of warmer air results in less cooling. Accordingly, coordination ofthe first and second fans in order to prevent inversion of the airflowfacilitates effective and efficient cooling.

FIG. 1C shows the first fan (120) and the second fan (130) beingoperated in a coordinated fashion. Accordingly, even though the airflowfrom the second fan (130) has been increased, the first fan (120)continues to expel air though an opening in the housing (110). Thisshows a high cooling demand condition being efficiently managed bycoordinating the behavior of the two cooling fans (120, 130).

Accordingly, the present specification describes, among other examples,a system for coordinating the performance of fans in a housing, thesystem including: a first fan, wherein the first fan is a power supplyfan; a second fan; a power supply; a control board to provide a firstpulsed wave modulated (PWM) signal to the second fan; and a logicelement to provide a control signal to the first fan by combining asecond PWM signal from the power supply and a third PWM signal from thecontrol board.

In another example, a system for enabling control panel regulation of afan, the system including a first fan; an OR-logic element that outputsa control signal to the first fan; a power supply to provide a firstpulsed wave modulated (PWM) signal to the OR-logic; and a controller toprovide a second PWM signal to the OR-logic. The second PWM signal isused to increase a duty cycle applied to the first fan so as to preventbackflow in air circulation when a second fan is operated.

These examples are illustrated and described as follows.

FIG. 2A shows a control arrangement a system for coordinating theperformance of fans in a housing, the system (200) including: a firstfan (120) for cooling a power supply (250); a second fan (130); acontrol board (240) to provide a first pulsed wave modulated (PWM)signal to the second fan (130); and a logic element (265) to provide acontrol signal to the first fan (120) based on a second PWM signal fromthe power supply (250) and a third PWM signal from the control board(240).

FIG. 2B shows a control arrangement (201) for integrating PWM controlsignals for the first fan (120). By providing the controller (240)managing the second fan (130) the ability to increase the effectivevoltage on the first fan motor, the controller (240) can increase theduty cycle applied to the first fan (120) when increasing the flow tothe second fan (130) in order to prevent inversion of airflow throughthe first fan (120). Also shown in FIG. 2 is the equipment (250) cooledby the first fan (120), the equipment (250) cooled by the first fan(120) may be electronics and/or a power supply. Control lines from thecontroller (240) and equipment (250) are provided to a logic element(260) for example, an OR-logic element. A control line is output fromthe OR-logic (260) to the first fan (120). This allows the equipment(250) to provide operational control over the first fan (120) withoutrelying on the controller (240) being operative. The OR-logic (260)and/or the first fan (120) may be external to the equipment (250).Alternately, the OR-logic (260) and the first fan may be internal to theequipment (250). For example, the equipment (250) may be a power supplywith an internal fan (120) and an internal OR-logic (260). In oneexample, the equipment (250) is a non-PMBus power supply module (PSM).

The controller (240) provides a pulsed width modulation (PWM) signal tothe OR-logic (260). The controller also provides a control signal to thesecond fan (130). The control signal to the second fan may be a PWMsignal. The control signal to the second fan may be a non-PWM signal.The controller (240) may have a look up table, either internally oraccessible. The lookup table considers the control signal provided bythe controller (240) to the second fan (120) and determines the PWMsignal for the controller (240) to output to the OR-logic (260) based onthe signal provided to the second fan (130). This allows the look uptable to compensate for the fan curves of the first fan (120) and secondfan (130), especially any differences in the two curves. In one examplethe signal provided to the second fan (130) is also provided to theOR-logic (260). In other examples, the signal provided to the second fan(120) by the controller (240) is different from the signal provided tothe OR-logic (240). The controller (240) may be mounted on a controlboard and/or may be part of a control board. The controller (240) may bea dedicated fan controller or may be a general purpose processor thatperforms a variety of tasks in addition to controlling the fan outputs.

As stated, the equipment (250) cooled by the first fan (120) may beelectronics and/or a power supply. The equipment (250) is mounted suchthat airflow produced by the first fan (120) passes over the equipment(250) to improve heat transfer from the equipment (250) to the air. Thefan (120) may be internal to the equipment (250). In some examples, theequipment (250) is a power supply with an internal fan, specifically,the equipment (250) is a non-PMBus power supply module (PSM).

The OR-logic (260) merges the control signals provided by the equipment(250) and the controller (240) to form a control signal provided to thefirst fan (120). In one example, the OR-logic (260) provides a controlsignal to both the first fan (120) and the second fan (130). In a secondexample, the OR-logic (260) provides a control signal to just the firstfan (120) and not the second fan (130). The control signals received andprovided by the OR-logic (260) may be PWM signals. The control signalsmay be power signals, where the peak voltage applied to the first fan(120) is also the peak voltage of the signal provided by the OR-logic(260). Alternately, the control signal provided by the OR-logic (260) tothe first fan (120) may have a lower voltage than the peak voltageapplied to the first fan (120). In this approach, the signal provided tothe first fan (120) may be used to regulate connection between the firstfan (120) and a power source.

The OR-logic (260) may output the control signal to the first fan (120)by synchronizing the received control signals from the controller (240)and the equipment (250). Synchronization may be performed using aseparate clock signal, by extracting a clock signal from a controlsignal, and/or by other suitable methods. In one example, thesynchronization is performed by delaying one signal until a level changeby the other signal.

As discussed below with respect to FIG. 3, the control signal from theequipment (250) and the controller (240) may operate of differentfrequencies. In some examples, the one control signal may have afrequency of at least 10 times the frequency of the other controlsignal. In some examples, the one control signal may have a frequency ofat least 100 times the frequency of the other control signal. In someexamples, the one control signal may have a frequency of at least 1000times the frequency of the other control signal. For example, thecontrol signal from the equipment (250) to the OR-logic (260) mayoperate in the kHz range while the control signal from the controller(240) to the OR-logic may operate in the MHz range (or vice versa).

The OR-logic (260) may be an electrical connection between the conductorcarrying the signal from the equipment (250) to the first fan (120) andthe conductor carrying the signal from the controller (240) to the firstfan (120). The electrical connection may be internal to the first fan(120), for example having a conductor from the equipment connected to anelectric motor powering the first fan (120) and a conductor from thecontroller connected to the electric motor powering the first fan (120).In one example, the electrical connection is a simple splice between twoconductors carrying the respective signals.

The OR-logic (260) may include components to prevent one control signalfrom being detected by the source of the other control signal. Forexample, the OR-logic (260) may include transistors (e.g. a field effecttransistor or FET) to isolate the two signals. Alternately, the OR-logic(260) may allow propagation of the signal from the equipment (250) tothe controller (240) and vice versa. In one example, the controllersamples the line between the controller (240) and the OR-logic (260) andmay determine the duty cycle provided by the equipment (250) to theOR-logic (260) based on this sampling. Similarly, the equipment (250)may sample the line between the equipment (250) and the OR-logic (260)and may determine the duty cycle provided by the controller (240) to theOR-logic (260) based on this sampling. The controller (240) or theequipment (250) may embeds signal information in the PWM signal providedto the OR-logic (260) that is detected by the equipment (250) orcontroller (240) respectively.

The OR-logic may receive PWM signals from the equipment (240) and thecontroller (240) and output a steady voltage DC signal to the first fan(120). In this approach, the OR-logic includes a component with arelatively high latency (which is to say, the component does not respondin the time frame of the individual pulses of the PWM input signals)between each of the lines from the controller (240) and the equipment(250) and the connection between the two input signal lines. In oneexample, the component is an electric motor of the first fan (120). Inanother example, the component is an inductor coil.

FIG. 3 shows one challenge with using a simple electrical connection toprovide the OR functionality. Namely, coordinating the PWM signals tocontrol the composite signal provided to the first fan (120). Onesolution to this is also shown. By combining a high frequency PWM signalwith a lower frequency PWM signal, the two signals do not need to besynchronized in order to assure a predictable output. However, theoutput is not a simple maximum relationship between the two inputs butrather uses the slightly more complex formula below.

Sig. A (Signal A) shows a PWM signal with a 50% duty cycle. Sig. B(Signal B) shows a second PWM signal with a 50% duty cycle at is theinverse of Sig. A. Combining Sig. A and Sig. B (Sig. A v B) can producea PWM signal with a duty cycle anywhere from 50% to 100% depending onthe degree to which the phases are synchronized. Thus, to the degreethat it is desired to combine the two different PWM signals to produce acomposite control signal, synchronization may be needed in order toachieve a predictable output.

Sig. C (Signal C) shows a higher frequency 50% duty cycle signal. Thisproduces the same output as either Sig. A or Sig. B when applied to anelectric motor as both have the same peak voltage and duty cycle.However, signal C can be combined with Sig. A and always produces thesame duty cycle without having to synchronize the signals (Sig. A v C).The duty cycle of the combined signals is1-((1-DutyCycleA)(1-DutyCycleC)). So combining two 50% duty cyclesproduces 1-(1-0.5)*(1-0.5) or a duty cycle of 75%. Accordingly, whilethe output duty PWM signal is not the same as either input PWM signal,the duty cycle of the combined signal is easily calculable. Accordingly,a PWM signal provided with a higher frequency can reliably producepredictable fan behavior.

While a 1 to 10 kHz frequency is generally sufficient for a PWM signalto be interpreted by an electric fan motor as a DC voltage, modernprocessors operate at much higher frequencies and can readily producemegahertz frequency control signals without additional hardware.

Other options include synchronizing the PWM signals between the twodifferent signal inputs. This avoids the uncertainty in the outputsignal. Synchronizing the input signals may be accomplished using acommon clock and/or introducing a delay into one line. Synchronizing theinput signals may also be accomplished by converting the signals to a DCvoltage before joining the two input signals. For example, by placing arelatively high latency element between the signal sources and thejunction between the signal lines. This allows a simple junction toprovide the desired OR functionality.

An example method consistent with this specification is illustrated inFIG. 4A. In FIG. 4A, a method (450) for controlling a power supply unit(PSU) fan, the method includes providing (460) a pulse width modulated(PWM) signal via a power line to regulate a speed of the fan, whereinthe PWM signal is formed using a PWM signal from a power supply and aPWM signal from a control board.

FIG. 4B shows a method (400) consistent with the present specification.Operation 410 is providing a pulse width modulated (PWM) signal from apower supply. Operation 420 is providing a PWM signal from a controlpanel. Operation 430 is combining the two PWM signals using an ORoperation. Operation 440 is using the combined PWM signal to controlpower application to a fan in a housing.

Operation 410 includes providing a pulse width modulated signal frompower supply. A pulse width modulated signal uses pulses of on and offto that switch between two voltages to produce an effective voltage in acomponent or device with a longer response time that the pulsefrequency. The amount of time the pulse is on is referred to as the dutycycle and is often expressed as a percentage. For example, a PWM signalwith a frequency of 100 Hz and a pulse length of 3 mS would have a dutycycle of 30%. PWM is an energy and equipment efficient method ofproviding tuned voltages to devices with longer response times.

Operation 420 includes providing a PWM signal from a control panel. Thefrequency of the PWM signal from the control panel and the power supplymay be the same. Alternately, the frequencies of the two signals mayhave different frequencies. In one example, the frequency of one signalis at least ten times the frequency of the other signal. In one example,the frequency of one signal is at least a hundred times the frequency ofthe other signal. In one example, the frequency of one signal is atleast a thousand times the frequency of the other signal.

Operation 430 includes combining the two PWM signals using an ORoperation. The use of the OR operation allows either signal toindependently increase the duty cycle in the output provided to the fan.In one example, the duty cycle of the output is equal to the larger ofthe two inputs signals such that, Duty cycle of theoutput=max(dutycycleA, dutycycleB). In another example, the duty cycleof the output is 1-((1-dutycycleA)*(1-dutycycleB)). Other variations arepossible, especially by applying the two duty cycles in an asynchronousmanner.

Operation 440 includes using the combined PWM signal to control powerapplication to a fan in a housing. In one example, the combined PWMsignal is use as the power source. In another example, the combined PWMsignal is used to regulate the on/off behavior of a power source.

In some examples, the signal from the control panel is provided to thepower supply as part of a multi-channel connection between the controlpanel and the power supply. The signal is then combined with the powersupply provided signal within the power supply with the output beingprovided to a power supply fan that cools the power supply. One notableadvantage of this approach is that in many instances, there is already amultichannel connection between the control panel and the power supplyand one of the channels can be used to provide this communicationwithout additional equipment costs. In some examples the signal isprovided from the control panel to the power supply with another signalbeing carried on the same line. This provides another way to provide thesignal as the response time needed for the fan may be much slower thanthe response time needed for other components in the system.Accordingly, in some approaches the ability to control the power supplyfan using the controller can be added to an existing design withoutadditional equipment or component costs. Because the OR-logic (260) canbe implemented in a variety of ways, the examples described in thisspecification can provide significantly increased cooling controlwithout increased costs.

FIG. 5 shows a control arrangement for integrating PWM control signalsfor the first fan (120). By providing the controller (240) managing thesecond fan (130) the ability to increase the effective voltage on thefirst fan motor, the controller (240) can increase the duty cycleapplied to the first fan (120) when increasing the flow to the secondfan (130) in order to prevent inversion of airflow through the first fan(120). FIG. 5 is the equipment (250) cooled by the first fan (120), theequipment (250) cooled by the first fan (120) may be electronics and/ora power supply. Control lines from the controller (240) and equipment(250) are provided to an OR-logic (260). A control line is output fromthe OR-logic (260) to the first fan (120). This allows the equipment(250) to provide operational control over the first fan (120) withoutrelying on the controller (240) being operative. In this example, thefirst fan (120) and the OR-logic (260) are located within the equipment(250). The equipment (250) includes a signal source (570) whichgenerates one of the pulse width modulated signals provided to theOR-logic.

FIG. 5 also shows the lines carrying four pulse width modulated signalsused to coordinate the first fan (120) and the second fan (130). Thefirst line (580) from the controller (240) to the second fan (130)carries a first PWM signal. The second line (582) carries a second PWMsignal from the signal source (570) in the equipment (250) to theOR-logic (260). The third line (584) carries a third PWM signal from thecontroller (240) to the OR-logic (260). The fourth line (586) carries afourth PWM signal from the OR-logic (260) to the first fan (120). Thefourth PWM signal is formed by the OR-logic (260) based on the secondand third PWM signals carried by the second line (582) and third line(584) respectively. The controller (240) coordinates the first PWMsignal and the third PWM signal carried by the first line (580) and thethird line (584) in order to coordinate the output of the second fan(130) and the first fan (120).

The equipment (250) may be a power supply. More specifically, theequipment (250) may be a non-PMBus power supply unit. Such power supplyunits may be more economical than power supplies with a PMBus but theirlack of a bus may make system control over the power supply fan (120)may make it challenging to coordinate the internal power supply fan(120) with other fans (130). The method and system described in thisspecification provide an economical and effective method of providingthis control.

The signal source (570) may be a processor and/or other component of theequipment (250). In some examples, the signal source (570) outputs thesame signal when the equipment (250) is powered. That is to say, theduty cycle output by the signal source (570) is not dependent on factorsother than the power state of the equipment (250). In other examples,the signal source (570) varies the duty cycle of the signal based oncircumstances. For example, the signal source (570) may have access totemperature information and may adjust the duty cycle of the outputsignal based on the temperature of the equipment (250).

It will be understood that, within the principles described by thisspecification, a vast number of variations exist. It should also beunderstood that the examples described are just examples, and are notintended to limit the scope, applicability, or construction of theclaims in any way.

What is claimed is:
 1. A system for coordinating cooling fans, thesystem comprising: a first fan for cooling a power supply; a second fan;a control board to provide a first pulsed wave modulated (PWM) signal tothe second fan; and a logic element to provide a control signal to thefirst fan based on a second PWM signal from the power supply and a thirdPWM signal from the control board.
 2. The system of claim 1, furthercomprising a lookup table which indexes the third PWM signal to thefirst PWM signal.
 3. The system of claim 1, wherein the second PWMsignal is independent of the third and first PWM signals.
 4. A systemfor coordinating cooling fans in a housing, the system comprising: afirst fan; an OR-logic element that outputs a control signal to thefirst fan; a power supply to provide a first pulsed wave modulated (PWM)signal to the OR-logic; and a controller to provide a second PWM signalto the OR-logic, wherein the second PWM signal is used to increase aduty cycle applied to the first fan so as to prevent backflow in aircirculation when a second fan is operated.
 5. The system of claim 4,wherein the OR-logic controls an electrical connection between the firstfan and a power source to power the first fan.
 6. The system of claim 4,wherein the OR-logical element comprises a transistor.
 7. The system ofclaim 4, wherein the first pulsed width modulated signal has a lowerduty cycle than the second PWM signal.
 8. The system of claim 4, whereinthe first fan operates when the controller is unpowered.
 9. The systemof claim 4, wherein the second PWM signal is provided on a line of amultiline connection between the controller and the power supply. 10.The system of claim 4, wherein the OR-logic is within the power supply.11. A method for controlling a power supply unit (PSU) fan, the methodcomprising: providing a pulse width modulated (PWM) signal via a powerline to regulate a speed of the fan, wherein the PWM signal is formedusing a PWM signal from a power supply and a PWM signal from a controlboard.
 12. The method of claim 11, wherein the PWM signal from thecontrol board varies based on an input to a second fan.
 13. The methodof claim 11, wherein the PWM signal from the control board is regulatedso as to prevent backflow of air through the power supply unit fan. 14.The method of claim 11, wherein the PWM signal from the control board isprovided on a channel of a multi-channel connector between the controlboard and the power supply.
 15. The method of claim 11, wherein the PWMsignal is output by an OR-logic element receiving the PWM signal from apower supply and the PWM signal from a control board.